Process for the vulcanization of rubber



?atented Oct. 17, 1933 PROCESS FOR THE VULCAN IZATION 0F Winfield Scott, Akron, ohm, assignor to The" RubberService Laboratories Company, Akron,

Ohio, a corporation of Ohio: 1

' No Drawing. ApplicationFebruary23,1927 a Serial No.[170 ,'4;19

"10 Claims. (01. 1s 5 s) My present invention is directed to the manufacture of vulcanized rubber by a process wherein there is employed as an accelerator of the Vulcanization step, the product obtained by'reactii ing an aldehyde in the presence of anacid upon a Schiffs base. The use of an accelerator of this type, as is hereinafter fully set forth and described, has been found to yield a fully vulcanized rubber product of high quality, in a shorter time and, if desired,'at lower temperatures. thanlare commonly employed in the vulcanization process.

7 It has been known for some time; that ,many simple condensation products of'equi-molecular proportions of aldehydes and amines, that is, compounds known as Schiffs bases possess prop erties that make themsusceptibl'e for use ,as accelerators in the vulcanization or rubber.;lTh e use of; such simple compounds as accelerators has been described in British Patent 7,370 of 1914 to Peachey and in United States Patent 1,417,970 l to Caldwell. The various aldehyde reaction prod.- ucts of the 'Schiffs bases. were later shown to be superior in accelerating power to the :simpler mono-molecular condensation products by North in a Patent-No.1,467',984 granted September 11, 1923.

In an earlier application, Serial No; 731,969 filed August 14, 1924, Ibhave. shown that the simple Schifls bases are capable of rearrangement or transformation when treated' with a small 'proportionof an acid which was subsequently neutralized and that theserearrangedor modified Schifis bases, when reacted with a further quantity of aldehyde, yielded products which comprised a class of active vulcanization accelerators capable of producing a vulcanized rubber V of high quality. V I have now further found, as is hereinafterset forth in detail, that a class of compounds closely i0 related to those described in my copendingapplismall proportions of a relatively weak acid, preferably an aliphatic organic acid preferablyQcontaining from four to ten carbon-atoms, with substantially two 'molecular'proportions Yof "analiphatic aldehyde; .The resulting products com- ,taking place. Alternatively,zthe reaction may be carried out in a closedcontainer and the ingredi .ents heated and reacted with one -'another under mately 0.5 to 3% by. weight, of the totalingredi tain the massat-a; temperature of approximately than-those set forth, thereis atendenc y' to proprise a class of accelerators of the rubber vulcanization process that are, rapid in theiraction and which aid in the production of a vulcanized rubber product of highquality, v

An example illustrative of one mode of manu- 5 a facturing an accelerator of; the type set forthis as follows: Substantially 73 parts (1 molecular proportion) of normal butyl amine are-reacted with approximately 72 parts (1 molecular proportion) a of butyl-aldehyde, The reaction iscarried out in a container equipped with a reflux condenser to return to, the container Iany vapors evolved therefrom by the heat liberated in the reaction the pressure of the evolvedvapors. Preferably;

-,the reaction product is-obtainedby employing a jacketed container supplied with suitable'heating and coolingmeansand causing thereaction to take place while maintaining the temperature ;of the ingredients and the product formed ata point below 40 C; The mixture is'maintained under these-conditions for approximately an hour to insurecomplete combination 'of the ingredi- Z5 ents therein. V ,7 The'reaction productis a-Schiffs baseand in .the case of thematerials mentioned'is'produced as is shown by the following equation:

t go+ornxcmnc=1-fnoina The Schiffs Tbase obtainedasrdescribed is then further reactedby combining one' molecularproportion of the base with substantially two molecu- 86 lar proportions (144 parts) of butyl-aldehyde. N This reaction is favored and the product obtained is improved in accelerating properties by the addition of small amounts, for example approxi-v ents present of anacidfofthe fatty acid series, such as butyric, Valerie, heptoic and the like.-

The reaction is preferably'carried out in a closed container equipped, with suitable means to, main- 80 to- 95-? 0. Although other temperatures may be employedrithas been found that at lower temperaturesthe desired reactiodproceeds rela-. tively slowly while at much-higher temperatures duce side reaction products. The heating conditions are preferably maintained for several hours and it has been found that very active accelerators are produced by this process after heating for as muchas forty hours as described. The extent of and time of heating varies, of course, with the quantity of material treated and upon the nature of the ingredients employed.

By proceeding in the manner as set forth there is obtained a reaction product of the aldehyde and the, Schiffs base. The product is then allowed to cool and the lower layer, comprising water of condensation, is separated from the reaction product obtained. This reaction product is then more completely dried, if necessary, in any suitable manner and the final product, compris ing a pale yellowish liquid is obtained.

An alternative procedure for manufacturing products of the type herein set forth is as follows Approximately equal molecular proportions of butyl-chloride and aqueous or alcoholic solutions of ammonia are reacted in a closed apparatus .at

a temperature of from 110 to 125 C. for a period of from four to eight hours. Any excess of ammonia is then removed from the mixture and the solution containing a mixture of butylaminehyd-rochlor'ides is evaporated nearly to dryness. The

calculated quantity of strong caustic'soda solu- -thoug h temperatures up to 100 C..may be em played without --seriously affecting the product obtained. After completion of this first reaction,

that is the production of a mixture :or 'schi'fl sbases, a quantity of butyl-a'ldehyde, substantial- :lytwice that used in the first step,-ismixed with from"one to 5'% its weig l'i t of an aliphatic acid preferablycontainingfrom 4 to 1 0 carbon atoms. -A 'second reaction commences at once accompanied by the evolution of heat and the elimination of water. when no further heat is evolved V the-mixture is warmed to a temperature of from i as to 95 C. and maintained at this point for a period of several hours. The resulting product, comprising a mixtureof water with an oily liquid insoluble therein, is then separated and the yellow oily liquid comprises the accelerator desired.

' -The water of "condensation produced in the first step of the reaction may be removed before adding the-aldehyde and acid mixture or it may be allowed to remain throughout the entire process and removed at the end of the operation.

Higher yields of n-butyl-amine may be realized aliphatic" aldehyde in the presence of approxi mately 1% of a straight chain aliphatic acid, However, when the acid is present in a mixture ofthis type, a portion thereof combines with the amine present to product a salt, which substances, and the Schiffs base produced therefrom, are non-accelerators of the rubber vulcanization process. Therefore, in order not to impair the accelerating power of the final product obtained, it is desirable'to operate the process as a two stage operation and preferably to have the acid present only. after the Schiffs base has been produced. I

Other aliphatic amines and other aliphatic aldehydes have been combined with one another in the presence of acids to produce an aldehyde derivative of a 'Schiifs base of the type hereinbefore set forth. Thus, in place of butylamine employed inthe example, other aliphatic amines such as the methylamines, ethylamines, propylamines, vinylamines, octylamines and other primary, secondary V and tertiary and aliphatic amines may be reacted with an aldehyde to produce a'Schiffs base, which base may then be combined with an aliphatic aldehyde-such as propionaldehyde, butylaldehyde, heptaldehyde, valericaldehyde and :the like in the presence of small proportions'of an organic acid such as propionic' acid, 'butyric acid, 'valerianic acid, vlieptylic acid and the'like to produce compounds of the type set forth; Although inorganic acids have been successfully employedin'place of the butyric acid used in the second stage of the process, I

have found that it is preferable to employ the weaker organic acids set forth.

The various products manufactured by the process hereinbefore described have been found to comprise a class of efficient and powerful ac celerators 'of the rubber vulcanization process which may be classified as semi-ultra accelerators. That the accelerators obtained in the present process produce fully vulcanized rubber products of high quality at lower temperatures andin a shorter vulcanization period than do most of the accelerators commonly employed. These preferred accelerators are not, howeven-so rapid in action as topreclude their use inmost commercial processes asis the case with the socalled ultra accelerators, which substances 'arerso very active as to cause an undesirable degree of .prevulcan'ization during the milling and other operating steps. The accelerators comprising the subject matter of my invention are then intermediate in their accelerating action between those substances commonly employed for that purpose and the so-called ultraaccelerators.

'One example illustrative of the use of my preferred accelerators is the following composition comprising a pure gum stock. Such a mix has been obtained by preparing in the well known manner a compound comprising: i

i Par-ts Smoked sheetrubber 1'00 Zinc oxide 5 Sulphur 3. 5 Accelerator '0. 5

as an accelerator, the reaction product obtained in the presence of 1% of butyric acid of two molecular parts of butyl-aldehyde on the Schiff base obtained by combining one molecular proportion of 'butylamine with an equivalent quantity of butylaldehyde was employed. The rubber mix was then vulcanized by heating in a press for about thirty minutesiat a temperature of approximately 258. F., that is a steam pressure Mineral rubber ;c e a Accelerator, preferably the butyl aldehyde of twenty pounds per square inch. The vulcaniz ed product on testing was found 'to have a mod- 'ulus ofelasticity'at 300% elongation of 251, at

500% elongation of 640, at 700% elongation of 2760, a tensile strength at break'of'4095 pounds per square inch and anulti'mate elongation of The physical characteristics of the vulcanized product which were obtained by heating in a press at a temperature given by forty pounds of steam pressure per square inch (287 F.) are as follows:

necessityQvary somewhat depending upon the ingredients used in the production of the comvpounds-"or upon the various compounding ingredients which may be employed in the rubber mix.

'Nordo I limitr'ny claims by any theories or statements advanced by wayof explanation of the changes involved nor to the exact method de scribed of producing'the accelerators employed in the process claimed.

What is-claimed'is: l. The process OfJnanufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of a small proportlon'of a compound obtained by treating substantially one molecular proportion ot a Schifis base produced by combining substantiallyequimolecular proportions of an aliphatic amine and analiphatic' aldehyde with an acid of the aliphatic series containing from four to ten carbon atomswhile simultaneously reacting said S'chiffs -base "with substantially two molecular proportions of an'aliphatic aldehyde. 2."The process of manufacturing "vulcanized rubber which comprises heating a mixture of Nb}- ber and 'sulphur'in-the presenceof a small proportion of a compound obtained by treating substantially one molecular proportion of a Schifis base produced by combining substantially equimolecular proportions of an aliphatic primary Modulus at elonga- 0P Ultimate Tensile at Time of cure break eliiiigla- 45 minutes 1723 3650 4225 580% 60 minutes 1868 3375 4240 500% It is apparent from the above, that a product of high commercial quality is produced by heating the rubber compound for approximately 45 minutes under the conditions set forth.

A hard rubber stock has also been manufactured in which accelerators of my new and pre-' ferred type have been employed. Such a stock comprises:

Parts Amber crepe rubber 20 Smoked sheet rubber 20 Lime 5 Zinc oxide 17.5 Sulphur 27.5 Mineral rubber 10 'One of my preferred accelerators 2 It was found that a hard rubber of excellent commercial qualities was produced after heating the rubber stock specified for approximately two hours at the temperature given by 40 pounds of steam pressure per square inch,

The examples hereinbefore given are to be understood as being illustrative only and not at all limitative of my process. Thus, the accelerators of the type herein disclosed and comprising the reaction product of two molecular proe portions of an aliphatic aldehyde in the presence of small proportions of an aliphatic acid upon a Schiffs base obtained by the condensation of an aliphatic amine with an aliphatic aldehyde may be used as vulcanization accelerators in other types of rubber compounds as are apparent to those'skilled in the art of rubber compounding. I do not limit my claims solely to the particular type of rubber compound employed nor to the definite amount of the accelerating compounds used in the rubber mix as such factors will, of

amine and an aliphatic aldehyde with from 1 to 3% by weight of an aliphatic acid containing at least four carbon atoms while simultaneously reacting said Schiifs base with substantially two .molecu'lar, proportions of an aliphatic aldehyde.

3. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of a small proportion of a compound obtained by treating substantiallyone molecular proportion of a Schifis base produced by combining substantially 'equimolecular proportions of a butylamine and butylaldehyde with approximately 1% by weight of butyric acid while simultaneously reacting said Schiffs base with substantially two molecular proportions of butyl-aldehyde. A

4. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of a small proportion of a compound obtained by treating substantially one molecular proportion of a Schifis base produced by combining substantially equi-molecular proportions of n-butylamine and n-butyl-aldehyde with approximately 1% by weight of butyric acid while simultaneously reacting said Schifis base with substantially two molecular proportions of n-butylaldehyde.

5. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of a small proportion ofa compound obtained bytreating a Schifis base produced by, combining substantially 73 parts by weightof n-butylamine and 72 parts by weight of n-butyl-aldehyde with approximately spar-ts by weight of butyric acid while simultaneously reacting and heat-treating said Schifis base with substantially 144 parts by weight of n-butyl-aldehyde.

6. A vulcanized rubber product obtained by heating rubber and sulphur in the presence of a q vulcanization accelerator, said accelerator comprising a compound obtained by treating substantially one molecular proportion of a Schifis base produced by combining substantially equi-molecular proportions of an aliphatic amine and an aliphatic aldehydev with an acid of the alipha Iii) ular proportions of an aliphatic primary-amine and an aliphatic aldehyde with from 1 to 3% by weight of an aliphatic acid containing at least four carbon atoms while simultaneously reacting said Schifis base with substantially two molecular proportions of an aliphatic aldehyde.

8. A vulcanized rubber product obtained by heating rubber and sulphur in the presence of a vulcanization accelerator, said accelerator comprising a compound obtained by treating substan-- tially one molecular proportion of a Schifis base produced by combining substantially equi-molecular proportions of a butylamine and butyl-aldehyde with approximately 1% by weight of butyric acid while simultaneously reacting said Schiffs base with substantially two molecular proportions of butyl-aldehyde. I

9. A vulcanized rubber product obtained by heating rubber and sulphur in the presence of a vulcanization accelerator, said accelerator com 7 prising a compound obtained by treating substantially one molecular proportion of a Schiif's base produced by combining substantially equimolecular proportions of n-butylamine and nbutyl-aldehyde with approximately 1% by weight of butyric acid while simultaneously reacting said Schifis base with substantially two molecular proportions of n-butyl-aldehyde. 10. A vulcanized rubber product obtained b heating rubber and sulphur in the presence of a 1 vulcanization accelerator, said accelerator comprising a compound obtained by treating a Schiifs base produced by combining substantially 73'parts by weight of n-butylamine and '72 parts by weight of n-butyl-aldehyde with approximately 3 parts by Weight of butyric acid while simultaneously reacting and heat-treating said Schifis base with substantially 144 parts by weight 01' n-butylaldehyde.

WINFIELD SCOTT. 

